It began with a desperate request for water and a Walmart employee’s suspicions about a tractor-trailer parked outside. That led officials on Sunday to discover at least 39 people packed into a sweltering trailer, several of them on the verge of death — their skin hot to the touch, their hearts dangerously racing — and eight men already dead. Another would die later at a hospital.

Authorities think they found an immigrant smuggling operation just 2½ hours from the Mexican border that ended in what San Antonio Police Chief William McManus described as a “horrific tragedy.” The victims, as young as 15, appeared to have been loaded like cargo into a trailer without working air conditioning during the height of the Texas summer. It was unknown how long they had been in the trailer or where their journey started, but 30 of the victims were taken to area hospitals and 17 had life-threatening injuries. Federal authorities said the victims were “undocumented aliens.”

Reyna Torres, consul of Mexico, confirmed in Spanish that Mexican nationals are among those dead and in the hospitals and said the consulate is interviewing the survivors.

City Fire Chief Charles Hood said some of the victims appeared to have suffered severe heatstroke, with heart rates soaring over 130 beats per minute. In the worst cases, Hood said, “a lot of them are going to have some irreversible brain damage”…